In the followings, the present invention will be described by referring mostly to its application inside blood vessels. Heart diseases among Japanese has been increasing year after year and it has now grown to be in the second place for the cause of death. Especially, unstable angina pectoris, acute myocardialinfarction, and inschemic heart sudden death are called as acute coronary syndromes, which are very serious diseases. Most of acute coronary syndromes are caused by thrombus formation triggered by a rupture of plaque of coronary artery.
Conventionally, invascular lesions including acute coronary syndromes are examined by nuclear medicine method. Nuclear medicine method is performed by utilizing radiopharmaceuticals accumulated in the subject part of the body, which have been administered beforehand. Diagnoses are carried out by detecting the radiation emitted from the radiopharmaceuticals accumulated in the target area by a detector generally placed outside the body and forming an image based thereon. Although the nuclear medical detection is inferior to CT and MRI as a morphologic diagnosis means, it is superior as a description diagnosis means for functions and tissue of living bodies. Therefore, it has been widely used in clinical examinations. On the other hand, nuclear medicine method devices have been proposed, in which a detector is inserted inside a human body for special purposes. However, these types exhibit a low sensitivity so that they are not used for actual diagnoses. Detectors which can be inserted to narrow blood vessels such as coronary arteries have not been developed so far.
The nuclear medicine method device for performing examinations by placing a detector outside the human body, and the nuclear medicine method device for performing examinations by inserting a detector inside the human body will be described in detail. The former nuclear medicine method device for performing an examination by placing the detector outside the body comprises a detector (in general, a gamma camera) outside the body for detecting the radiation emitted from the radiopharmaceutical administered beforehand and a computer for forming an image based on detected signals. The detector comprises a scintillator and some ten photomultipliers provided inside. Emission of light is caused upon incidence of the radiation to the scintillator emitted from inside the body and the light signals are transmitted to the photomultipliers corresponding to the positions to be converted to electric signals. The signals are formed into images by a computer to be used for diagnoses.
In this nuclear medicine method device, the detector is placed outside the body so that there is a distance between the detector and the target body part. Thus the radiation is scattered and attenuated by the distance and the living body tissue present in between, thereby causing deterioration of the resolution. Also, when the target is the one that is moving such as the heart, deterioration of the resolution cannot be avoided. The maximum resolution is about 5 mm. Therefore, it is impossible to discriminate a very small accumulation of the radiation in the case of, for example, lesions inside the coronary arteries from other radiations. Further, the device is on a large-scale, so that it is very hard to be used in emergency cases such as in a room for the heart catheter where acute coronary syndromes are treated.
There are nuclear medicine method devices in which the detector is miniaturized to be inserted inside the body for a special purpose. However, they are not used practically. As an example of this type of the device, U.S. Pat. No. 4,595,014 discloses an intracavity radiation detector. A collimator formed by a substance such as tungsten is mounted onto the device for obtaining the directivity of the radiation entering into the scintillator. In this case, it is necessary to thicken the collimator especially for the radiation with high energy in order to increase the directivity of the incoming radiation. The volume of the scintillator is reduced and the sensitivity is deteriorated as the thickness of the collimator is increased. Also, the detector of the above-described detection device cannot be inserted into narrow vessels of the living bodies.
As another example of the device in which the detector is inserted inside the body for performing an examination, Japanese Patent Unexamined Publication No. 5-11055 and Japanese Patent Unexamined Publication No. 8-94760 disclose luminal radiation detectors. In these devices, two scintillators with the diameter of about 8 mm are arranged in parallel or in vertical and optical fibers are connected to each scintillator for guiding the light signals to two photomultipliers so as to detect only the coincident signals. Thereby, background is reduced and, at the same time, the directivity of the incoming radiation is obtained. In this method, different light signals by the radiations emitted from different scintillators are coincided so that the background can be reduced. However, the sensitivity for γ-ray becomes low since it is very rare that one photon such as γ-ray makes both scintillator emit the light. Therefore, it is impossible with the method to miniaturize the scintillator to be able to be inserted into the blood vessels.